A valve timing control apparatus configured to change an opening and closing timing of each of an intake valve and an exhaust valve depending on an operation condition of an internal combustion engine (which will be hereinafter referred to as an engine) has been developed. Such valve timing control apparatus includes, for example, a configuration for changing a relative rotation phase of a driven-side rotation member relative to a driving-side rotation member that rotates by an engine operation so as to change the opening and closing timing of each of the intake valve and the exhaust valve opening and closing in association with the rotation of the driven-side rotation member.
An optimum opening and closing timing of the intake valve and the exhaust valve depends on the operation condition of the engine, for example, depends on whether the engine is started or a vehicle is being driven. At a time of the engine start, the relative rotation phase of the driven-side rotation member relative to the driving-side rotation member is locked at a predetermined phase so as to realize the optimum opening and closing timing of the intake valve and the exhaust valve for the engine start. At this time, however, in a case where the relative rotation phase is maintained at the aforementioned predetermined phase during idling of the engine after the engine start, hydrocarbon emissions (HC emissions) may increase. Thus, during the idling of the engine after the engine start, the relative rotation phase is desired to be changed to a certain phase at which the HC emissions may be restrained.
WO2011/055589A1, which will be hereinafter referred to as Reference 1, discloses a valve timing control apparatus that includes a housing serving as the driving-side rotation member connected to a camshaft, and an inner rotor serving as the driven-side rotation member provided at an inner portion of the housing. According to the valve timing control apparatus disclosed in Reference 1, fluid chambers are formed by the housing and the inner rotor. Each of the fluid chambers is divided into a retarded angle chamber and an advanced angle chamber by a vane serving as a partition portion. The valve timing control apparatus also includes an oil control valve (OCV) for shifting the relative rotation phase of the inner rotor relative to the housing in a retarded angle direction or an advanced angle direction by selecting either the retarded angle chambers or the advanced angle chambers to supply hydraulic oil to the selected chambers. Further, a torsion spring is arranged between the inner rotor and the housing for generating a biasing force so that the relative rotation phase is shifted in the advanced angle direction.
The valve timing control apparatus disclosed in Reference 1 includes two intermediate lock members provided at the housing to be projectable and retractable relative to the inner rotor and single intermediate lock groove formed at the inner rotor so that each of the intermediate lock members is inserted to be fitted to the intermediate lock groove. Each of the intermediate lock members projects to the intermediate lock groove by a biasing force of a spring. An intermediate lock passage is formed at the inner rotor to apply a pressure of hydraulic oil in a direction in which each of the intermediate lock members is retracted from the intermediate lock groove.
A most retarded angle lock member is provided, separately from the intermediate lock members, at the housing. A most retarded angle lock groove is formed, separately from the intermediate lock groove, at the inner rotor so that the most retarded angle lock member is inserted to be fitted to the most retarded angle lock groove. The most retarded angle lock member projects to the most retarded angle lock groove by a biasing force of a spring. A most retarded angle lock passage is formed at the inner rotor to apply a pressure of hydraulic oil in a direction in which the most retarded angle lock member is retracted from the most retarded angle lock groove.
The relative rotation phase of the inner rotor relative to the housing in a case where the intermediate lock members are fitted to the intermediate lock groove is defined as an intermediate lock phase. A state in which the relative rotation phase is arranged at the intermediate lock phase is defined as an intermediate lock state. In addition, the relative rotation phase of the inner rotor relative to the housing in a case where the most retarded angle lock member is fitted to the most retarded angle lock groove is defined as a most retarded angle phase. A state in which the relative rotation phase is arranged at the most retarded angle phase is defined as a most retarded angle lock state.
The valve timing control apparatus disclosed in Reference 1 includes an oil switching valve (OSV) that operates independently from the OCV so as to cause the intermediate lock members to retract from the intermediate lock groove. Because of the OCV and the OSV, the relative rotation phase at the start of the engine is locked at the intermediate lock phase at which startability of the engine is improved. During idling of the engine after the engine start, the relative rotation phase is displaced in the retarded angle direction to be locked at the most retarded angle phase at which hydrocarbon emissions (HC emissions) are restrained.
In the valve timing control apparatus disclosed in Reference 1, in order to obtain smooth projection and retraction of each of the intermediate lock members and the most retarded angle lock member, the inner rotor may rotate relative to the housing by a small angle in the intermediate lock state. Specifically, an angle formed by opposing wall surfaces of the intermediate lock groove in a circumferential direction is slightly greater than an angle formed by respective outer side surfaces of the intermediate lock members in the circumferential direction. A difference between the aforementioned angles will be hereinafter referred to as a first clearance angle. In addition, the inner rotor also rotates relative to the housing by a small angle in the most retarded angle lock state. Specifically, a clearance is formed between a side surface of the most retarded angle lock member at a retarded angle side and a wall surface of the most retarded angle lock groove at the retarded angle side in a state where the vane is in contact with a protruding portion of the housing in the most retarded angle phase. An angle corresponding to the aforementioned clearance will be referred to as a second clearance angle. In the valve timing control apparatus, the first clearance angle and the second clearance angle are basically the same angle.
Because of the first clearance angle and the second clearance angle, however, the inner rotor and the housing move relative to each other by a small amount in the advanced angle direction and the retarded angle direction alternately due to a torque fluctuation of the camshaft, for example, in the intermediate lock state or the most retarded angle lock state. As a result, a hitting sound occurs between the housing and the inner rotor. Such sound is greater in the most retarded angle lock state than in the intermediate lock state because of the following two reasons. First, while a source of hitting sound in the intermediate lock state is mainly a collision between each of the intermediate lock members and the intermediate lock groove, a source of hitting sound in the most retarded angle lock state is a collision between the vane and the protruding portion. At this time, an area at which the vane is collided with the protruding portion is greater than an area at which the intermediate lock members are collided with the intermediate lock groove. Second, in the configuration in which the intermediate lock member projects and retracts in a radial direction relative to a rotation axis as in the valve timing control apparatus disclosed in Reference 1, a portion at which the vane is collided with the protruding portion is closer to an outer side of the valve timing control apparatus than a portion at which each of the intermediate lock members is collided with the intermediate lock groove. Therefore, a collision speed of the vane and the protruding portion is greater than a collision speed of each of the intermediate lock members and the intermediate lock groove, which results in a greater hitting sound. In view of reduction of hitting sound in the most retarded angle lock state, an improved valve timing control apparatus may be desirable.
A need thus exists for a valve timing control apparatus which is not susceptible to the drawback mentioned above.